The present invention relates to the field of two-phase flow measurement. In particular, the present invention provides a method and apparatus for measuring the relative quantities of gas and liquid in a flowing fluid stream, especially for the measurement of wet steam.
One method of enhancing recovery of hydrocarbons in, for example, oil-bearing reservoirs, is to inject steam. In order to properly manage this enhanced recovery technique, it is necessary to know the "quality" and the mass flow rate of steam that is injected, wherein the "quality" is defined as the ratio of vapor to vapor plus liquid of the injected steam.
Many methods have been proposed for the measurement of steam quality in surface steam lines. For example, U.S. Pat. No. 4,662,219, to Nguyen, incorporated by reference herein for all purposes and assigned to the assignee of the present invention, discloses a method of using two orifice plates in series to determine steam quality. However, such methods actually provide only an indirect determination of steam quality because they are not directly measuring the mass and/or density of the liquid stream. They are in many cases only accurate over a limited range of conditions.
U.S. Pat. Nos. 4,689,979 and 4,773,257 to Aslesen et al., also assigned to the assignee of the present invention and incorporated herein by reference for all purposes, discloses a method of measuring the relative amounts of oil and water in a liquid stream. However, no method of determining steam quality is shown or suggested.
A "Q-Bar" device has also been described as being useful in the measurement of two phase streams. For example, the "Steamcheck Energy Monitor" sold by Baker Packers uses the "spike" resonant frequency of a resonating tube to determine steam quality. This device uses only a sample of the steam and has found to have only limited accuracy.
It is desirable, therefore, to devise an improved method of measuring wet steam.